DESCRIPTION (from applicant's abstract): Mutations in FBN1 result in the pleiotropic cardiovascular, skeletal, and ocular phenotypic features of the Marfan syndrome as well as in several of the individual phenotypic features of the Marfan syndrome in isolation, such a isolated aortic aneurysm, isolated ectopia lentis, and isolated tall statures. Mutations have also been found in Shprintzen-Goldberg syndrome and the MASS phenotype, and FBN1 has been implicated in Weill-Marchesani syndrome, pseudoexfoliation of the lens, and scleroderma. More than 200 different mutations in FBNl have bee identified. Mutations in FBN2 have been identified in individuals with congenital contractural arachnodactyly, disorder affecting skeletal but usually not ocular or cardiovascular tissues. With the notable exception of the mutations causing "neonatal" Marfan syndrome, efforts correlate genotype with phenotype been unsuccessful. In this application, two potential mechanisms by which mutations in fibrillins may result in disease are proposed. In the first case, mutant fibrillin molecules would create weak spots in all microfibrils; over time, microfibrils, which are normally very long, would be fragmented into short microfibrillar pieces, precipitating a cascade of events leading to the development of disease. A second possible mechanism is based on the hypothesis that some mutations in fibrillins will inhibit assembly of microfibrils. In this case, most of the microfibrils will be short, and severe early onset disease is predicted. Specific aims are proposed to test these mechanisms of disease pathogenesis. In the first specific aim, novel "coculture assay" will be utilized to precisely define domains in fibrillins required for assembly of microfibrils. In this assay, effects of epitope-mapped monoclonal antibodies will be monitored, and cells transfected with both wildtype and mutant constructs will be tested. In the second specific aim, in order to test whether the results obtained in the first specific aim hold within the context of full-length fibrillin, fibrillin constructs containing selected mutation will be overexpressed in cells which assemble overexpressed wildtype fibrillin into fibrils. In addition, selected mutant constructs will be tested for protease susceptibility in comparison to analogous wildtype constructs.